Moves by the NZ Transport Agency to play down opponents' views on the Basin Reserve flyover have been firmly slapped down by the board deciding whether it will be built.

Battle lines have been drawn after the agency laid out its case yesterday on the first day of the board of inquiry's eight-week hearing for resource consent.

The four-member board, led by retired judge Gordon Whiting, was quick to clarify that the views of opponents and lay people would carry weight in the decision-making.

Day one was largely taken up by lawyers for the agency setting the legal boundaries that will determine how the rest of the hearing plays out. But the board was not shy about setting boundaries of its own.

Agency lawyer Andrew Cameron told the board to be careful when considering non-expert evidence, as some submitters could be relying on questionable information to support their claims.

Judge Whiting was confident in the board's ability to tell the difference between an expert and a lay person. But he added that the latter, particularly those who lived in the Basin area, would add just as much value to the hearing.

"They may not be expert witnesses . . . but their views and how they perceive the beauty of the area where they live can be equally as telling as the evidence of an architect."

Cameron stressed that the agency was not looking to pick a fight during the hearing with those who oppose the flyover.

He told the board its members had been appointed to decide whether the flyover proposal satisfied the conditions of the Resource Management Act, not to referee a scrap. "This is not a contest between litigants."

But whether or not the agency wants a fight, it may get one. The board received 215 submissions, with 83 per cent opposing the flyover in full or in part.

Common ground between parties on either side of the debate also appears sparse. Judge Whiting said 130 contested issues still needed to be teased out.

"This is unwieldy and must be addressed during the hearing."

Among all the legal wrangling, lawyers for the agency also summarised the main reasons why it wants to build a $90 million flyover 20 metres north of the Basin Reserve.

Relieving congestion, giving pedestrians, cyclists and public transport more room to move, and injecting more money into Wellington's coffers by creating jobs and improving freight efficiency were among the major benefits.

But the opening exchanges also gave an insight into where the hearing could turn into a battle.

Cameron spent some time reminding the board it did not have the power to choose an alternative to the flyover.

"The executive responsibility for selecting sites, routes, and methods remains with the Transport Agency."

Methods the agency used to rule out alternatives, such as a tunnel or improvements to the existing roundabout, were criticised by the board's independent advisers in a recent peer review of the agency's evidence.

But Judge Whiting said that if the board did decide the agency had done a poor job of considering alternatives it could still use that view to inform its overall decision. "This issue has clearly been raised by a number of submitters," he said.